This program project seeks to enhance the ability of ultrasonic imaging to detect and characterize tumors. This area was chosen because of the widespread use of ultrasonic imaging in practically all specialties and medical environments. The improvements that we seek, selected to make ultrasonic imaging even more useful, would thus have a large impact on medical practice. They would contribute to oncology through improved detection, diagnosis and treatment monitoring. The program consists of three projects that take different approaches to the problem of collecting and processing data to form images. These projects are based on new approaches as well as on adaptations of approaches that have been successful in industrial non-destructive testing and in optics. Our program is also based on laboratory and clinical cores for assuring interaction and co-ordination between the projects and between imaging modalities (US, CT and MRI) and pathology. This structure should remove many of the problems that have been encountered when attempting to improve the ultrasonic tissue characterization through individual research projects. Also, the clinical collaborators will benefit from having available a variety of image formation methods to evaluate for different purposes. The inter-comparison with other modalities can thus be efficiently handled. One project will gather animal and human in-vivo data on the ultrasonic properties of tissues and tumors. These data will be used to assess the accuracy of the quantitative methods being developed for clinical use. Another project will be assessing the often neglected effects of anisotropy in tissue properties on present and future imaging methods, as well seek to use such effects to characterize tissues. To assure that this program remains current as ultrasonic methodology advances during the term of the grant we have included work in related areas. Some type of contrast agent will most likely be widely used in the near future. Therefore we have included a project that will be developing a promising new contrast agent. This project will allow us to gain experience with characterizing these materials and offer guidance on the use of contrast in enhancing image features associated with tumors. Questions of patient safety must not be ignored. A transducer and measurement system project has been included so that we will be able to refine our ultrasonic dosimetry methods. This project also will develop transducers for wideband data collection that is needed for accurate modeling, essential for developing new methods, and high frequency transducers for the new areas of skin and intraluminal